1. Technical Field
The present disclosure relates to recording paper supply device or to a roll paper printer having a recording paper supply device that pulls and supplies recording paper from a paper roll held in a roll paper compartment, and relates more particularly to a recording paper supply device or a roll paper printer having a detection unit that detects when the amount of recording paper on the paper roll in the roll paper compartment becomes less than a specific amount (a near-end state), and to a method of detecting a near-end state.
2. Related Art
Roll paper printers typically store a roll paper having continuous recording paper wound into a roll in a roll paper compartment, and print while pulling and conveying the recording paper from the paper roll through the conveyance path. Some users of such printers would like advance warning that the paper roll is near the end and the printer will soon be unable to print. Detecting that the recording paper is near the end (detecting a near-end state) before the paper supply is depleted so that a replacement roll can be readied is particularly desirable for users of roll paper printers used to produce receipts because the inability to produce a complete receipt is especially inconvenient. Methods of detecting a near-end state based on the position of the core or the outside surface of the paper roll in the roll paper compartment have therefore been conventionally used to meet this need.
Some roll paper printers use a limit switch or other mechanical sensor in the roll paper compartment to detect a near-end state. Because the outside diameter of the paper roll decreases as the remaining amount of recording paper decreases, this detection method is based on the position of the outside surface of the paper roll moving to the inside circumference side, or the position of the core descending. For example, when the position of the core is not fixed and the paper roll is loaded by simply dropping the paper roll into the roll paper compartment, the paper roll normally rests of its own weight on the bottom of the roll paper compartment, and the position of the core descends as the outside diameter of the paper roll decreases. A near-end state can therefore be detected when the core descends to the position of a detection lever.
However, with a drop-in loading roll paper compartment, the paper roll may become loose inside the roll paper compartment because the core is not affixed, possibly resulting in being unable to deliver the recording paper smoothly and the recording paper becoming skewed. A construction that holds the paper roll between a pair of side panels to hold the paper roll with side pressure applied may be used to enable smoothly delivering roll paper from the roll and prevent skewing. JP-A-2009-102129 discloses a roll paper printer having a roll paper compartment with this type of structure.
The roll paper printer disclosed in JP-A-2009-102129 has a pair of left and right side panels in the roll paper compartment, and a pressure member that is urged to the inside widthwise by a spring is attached to one of the side panels. The paper roll is disposed between this pressure member and the other side panel and held by the urging force of the spring.
In a configuration that holds the paper roll between a side panel and a pressure member as disclosed in JP-A-2009-102129, friction occurs between the side of the paper roll and the side panel or the pressure member. More specifically, the position of the paper roll is determined by the balance of the three forces that work on the paper roll in the roll paper compartment: the upward-pulling force of the recording paper that is pulled from the paper roll, the force of gravity corresponding to the weight of the paper roll, and the friction produced with the side panel or pressure member.
When a large amount of recording paper remains, the paper roll is heavy. Therefore because the force of gravity exceeds the friction, the paper roll will drop and return to the bottom of the roll paper compartment even if the paper roll is lifted off the bottom of the roll paper compartment by the force pulling the paper from the roll. However, when little roll paper remains on the roll, the weight of the paper roll also decreases, and if paper is pulled from the roll and the paper roll is lifted off the bottom of the roll paper compartment, the paper roll may remain in that position by friction and not drop back to the bottom of the compartment. As a result, the paper roll gradually rises in the direction the recording paper is pulled as recording paper is pulled from the paper roll. The outside of the paper roll may therefore end up touching the roller (delivery roller) around which the delivered recording paper travels.
When the paper roll is held between side panels to enable smooth delivery of the roll paper, the paper roll may thus rise in the roll paper compartment as the remaining amount of recording paper decreases. A near-end state can therefore not be detected using a sensor that operates on the assumption the paper roll is resting on the bottom of the roll paper compartment. More specifically, even if the detection lever is located at a height near the bottom of the roll paper compartment based on the assumption that the position of the core will descend as the remaining amount of recording paper decreases, the core will not contact the detection lever because the core rises with the paper roll. Detecting a near-end state may therefore not be possible with the detection lever located as described above.
The roll paper printer described in JP-A-2009-102129 has a structure that prevents the paper roll rising from the bottom of the roll paper compartment. More specifically, in JP-A-2009-102129, the delivery roller is located at the bottom of the roll paper compartment, and a guide roller is located on the opposite side of the roll paper center as the delivery roller. The outside surface of the paper roll is always in contact with the delivery roller and the guide roller, and the parts are located so that the force of the recording paper delivered from the paper roll positioned in contact with the guide roller causing the paper roll to rise acts as the force moving the paper roll to the delivery roller side.
While this configuration can prevent the paper roll from rising in the roll paper compartment, and enables detecting a near-end state with a sensor located as described in the literature, the construction of the roll paper compartment is complicated. More specifically, this configuration uses a plurality of guide rollers and a delivery roller, and these rollers must be disposed in specific relative positions. The freedom of design is therefore low, and reducing the number of parts, device size, and cost is difficult.